docs: def cortex_rgba_plot_2D(the_map, rgba, axes=None, triangulation=None):
      '''
      cortex_rgba_plot_2D(map, rgba, axes) plots the given cortical map on the given axes using the
        given (n x 4) matrix of vertex colors and yields the resulting polygon collection object.
      cortex_rgba_plot_2D(map, rgba) uses matplotlib.pyplot.gca() for the axes.
  
      The option triangulation may also be passed if the triangularion object has already been
      created; otherwise it is generated fresh.
      '''
      cmap = colors_to_cmap(rgba)
      zs = np.linspace(0.0, 1.0, the_map.vertex_count)
      return cortex_cmap_plot_2D(the_map, zs, cmap, axes=axes, triangulation=triangulation)